Before starting you should make sure that your PHP version is up to date:
Use Composer to install Cakephp 3 Framework,
Composer is officially supported method for Installation, so download composer at, Composer (Windows/Linux/Mac)
Run this to Install cakephp,
php composer.phar create-project --prefer-dist cakephp/app my_app_name
Once Composer finishes downloading the application skeleton and the core CakePHP library, you should have a functioning CakePHP application installed via Composer. Be sure to keep the composer.json and composer.lock files with the rest of your source code.
Or follow this easyest way to install cakephp
Follow the bellow steps,
By default, without any arguments provided, this will serve your application at http://localhost:8765/.
fire this at your browser, http://example.com/ or http://localhost:8765/. At this point, you’ll be presented with CakePHP’s default home, and a message that tells you the status of your current database connection and you are ready for your first application.
For more details on Installation and Setup follow, Cakephp 3.X Installation